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PRACTICAL ORGANIC CHEMISTRY

PREPARATION in.

Isatin.—The   formation   of   isatin   from   indigo   may  be
represented as follows :—

/CO,

O   ; O

Indigo.

/CO ,
<X      ^>CO.

Pscudo-isatin.

This compound represents the unstable psetido- or lactam-
form, and passes into the stable or lactim-form (Baeyer),

-CO.

Isatin (stable form).

There exists, however, some uncertainty as to which formula
represents the stable form. Derivatives of both forms are
known, and the compound offers an example of iautomcrism
(see Notes on Preps. 16, p. 252), or, as it has been also termed,
pscudomerism*

The constitution of isatin has been determined by its synthesis
from ^-nitrophenylglyoxylic acid,

CBH4<

/CO.COOH

/CO.COOH

Q,H4

/CO,

I
f

iiii

which passes on reduction into the amino-compound, the latter
forming the anhydride or isatin (Claisen).

PREPARATION 112.
Quinoline.—The formation of quinoline by "Skuaup's
reaction" may be explained as follows : The sulphuric acid
converts the glycerol into acrolein, which then combines with
the aniline to form acrolein-aniline. The latter on oxidation
with nitrobenzene yields quinoline.                                      "»